Interfering diffusive photon-density waves with an absorbing-fluorescent inhomogeneity

Review of structured light in diffuse optical imaging

Diffuse optical imaging probes deep living tissue enabling structural, functional, metabolic, and molecular imaging. Recently, due to the availability of spatial light modulators, wide-field quantitative diffuse optical techniques have been implemented, which benefit greatly from structured light methodologies. Such implementations facilitate the quantification and characterization of depth-resolved optical and physiological properties of thick and deep tissue at fast acquisition speeds. We summarize the current state of work and applications in the three main techniques leveraging structured light: spatial frequency-domain imaging, optical tomography, and single-pixel imaging. The theory, measurement, and analysis of spatial frequency-domain imaging are described. Then, advanced theories, processing, and imaging systems are summarized. Preclinical and clinical applications on physiological measurements for guidance and diagnosis are summarized. General theory and method development of tomographic approaches as well as applications including fluorescence molecular tomography are introduced. Lastly, recent developments of single-pixel imaging methodologies and applications are reviewed.

Improving mesoscopic fluorescence molecular tomography via preconditioning and regularization

Mesoscopic fluorescence molecular tomography (MFMT) is a novel imaging technique capable of obtaining 3-D distribution of molecular probes inside biological tissues at depths of a few millimeters with a resolution up to ~100 μm. However, the ill-conditioned nature of the MFMT inverse problem severely deteriorates its reconstruction performances. Furthermore, dense spatial sampling and fine discretization of the imaging volume required for high resolution reconstructions make the sensitivity matrix (Jacobian) highly correlated, which prevents even advanced algorithms from achieving optimal solutions. In this work, we propose two computational methods to respectively increase the incoherence of the sensitivity matrix and improve the convergence rate of the inverse solver. We first apply a compressed sensing (CS) based preconditioner on either the whole sensitivity matrix or sub sensitivity matrices to reduce the coherence between columns of the sensitivity matrix. Then we employed a regularization method based on the weight iterative improvement method (WIIM) to mitigate the ill-condition of the sensitivity matrix and to drive the iterative optimization process towards convergence at a faster rate. We performed numerical simulations and phantom experiments to validate the effectiveness of the proposed strategies. In both in silico and in vitro cases, we were able to improve the quality of MFMT reconstructions significantly.

Dental optical tomography with upconversion nanoparticles-a feasibility study

Upconversion nanoparticles (UCNPs) have the unique ability to emit multiple colors upon excitation by near-infrared (NIR) light. Herein, we investigate the potential use of UCNPs as contrast agents for dental optical tomography, with a focus on monitoring the status of fillings after dental restoration. The potential of performing tomographic imaging using UCNP emission of visible or NIR light is established. This in silico and ex vivo study paves the way toward employing UCNPs as theranostic agents for dental applications.

Contrast-enhanced near-infrared (NIR) optical imaging for subsurface cancer detection

Synergistic efforts in the developments of molecular specific imaging probes and advancements of optical imaging technologies (including the novel instrumentation and imaging algorithms) that lead to a new tool for early disease diagnosis and drug discovery are described.

Adaptive calibration for object localization in turbid media with interfering diffuse photon density waves

The amplitude cancellation method that uses dual out-of-phase sources (a phased array system) can sensitively detect and locate small objects in turbid media. The balance of these two sources is crucial to the system's detection sensitivity and accuracy. We describe a convenient method with which to adaptively calibrate the amplitudes of the two sources at each scanning position by use of low-frequency modulation of the intensity of the in-phase and the antiphase sources. We achieve accurate localization ability of the phased array system by accounting for the influence of asymmetrical boundaries and the heterogeneous background absorption. Experimental data on human breast phantoms demonstrate that localization accuracy within several millimeters has been accomplished through this method.

Detection limit enhancement of fluorescent heterogeneities in turbid media by dual-interfering excitation

We report on a quantitative comparison between the single-source and the dual-interfering-source configurations for the detection of fluorescent heterogeneities embedded in a piecewise highly scattering homogeneous fluorescent background. The study is based on simulations with analytical solutions of the frequency-domain fluorescent diffuse photon density waves and practical signal-to-noise ratio considerations. Results show that dual-interfering sources outperform single-source techniques for the detection of heterogeneities in terms of fluorophore concentration and lifetime contrast. To detect the same inhomogeneity, less concentration and lifetime contrast is required with dual-interfering sources.